The present invention generally relates to magnetic storage devices and particularly to a method and apparatus for increased mechanical stability of a tape within its cartridge when locked in an operating position and also during handling, storage and shipping.
It is of crucial importance in linear recording that the magnetic head be precisely positioned relative to the magnetic tape. This is important both during writing, when the tracks are to be positioned according to a standardized track table that defines the exact position of each track, or during reading when the head has to be positioned exactly on the track in order to avoid interference from adjacent tracks to avoid read errors. Proper positioning avoids the need for electronic error correction or time-consuming re-read operations.
In order to exactly position the tracks during a writing operation, a reference position is needed so that the tracks are positioned relative to that reference. This reference may be a fixed point inside the drive. If the position of the cartridge as well as the position of the magnetic head are precisely located with respect to this point with a given tolerance, and the tape is referenced to the cartridge, i.e., precisely located with respect to the cartridge, an unambiguous correlation can be established between the magnetic head and the tape position. The problem with this method of positioning the head and the tape is that tolerance build-up reduces the accuracy by which the magnetic storage device is able to position the tracks during a writing operation.
To solve this problem, a commonly used method is to position the tracks relative to one of the edges of the magnetic tape. To determine the position of the tape edge, the magnetic tape device may measure the amplitude from the read head, at the same time as the magnetic head is stepped across a position where the tape edge is expected to be found. The position where the tape edge is calculated, based on that measurement, is then defined as a reference point.
Using this method, various tolerances are eliminated and the position by which the tracks may be positioned onto the tape is increased considerably. However, it is noted that the success of the described method, and the precision that is obtained in positioning of the tracks that are written onto the tape, will depend on the degree the position of the tape varies relative to the cartridge and also on the degree a cartridge may be locked into a fixed position relative to the magnetic head. These two factors are of great importance to allow an increase in track density and thus the ability to meet the demands of higher storage capacity.
Variations in tape position relative to its cartridge is dependent upon various factors, such as the precision of the tape guiding mechanism and the precision of the slitting process during manufacture of the tape. Another factor of importance is the mechanical stability of the tape hubs, as vibrations in these hubs can be transferred to the tape. The components in this vibration that are perpendicular to the direction of normal movement of the tape will be transferred from the hubs to the place where the magnetic head is located, although the amplitude of this vibration may be reduced through the guiding mechanism. Since the first harmonic rotation frequency of these components may be in the order of magnitude of 50-100 Hz, it is evident that the stability of the hubs is important for the stability of the tape position.
The most direct way of controlling the tape position in this respect is to stabilize the cartridge as close as possible to the place where the hubs are located, since this is the place in the cartridge where most of the mechanical energy of movement or momentum is encountered. A method in use today for stabilization of the hubs includes use of a spring that presses the hubs down against the base cover of the cartridge. However, the spring force used is typically not very large in order to limit the friction and thus heat generation within the cartridge. It is also relatively small compared to the forces that are produced as a result of the rotational movement by the tape hubs. Furthermore, the cartridge is fixed in positions that are typically far from the center of the tape hubs. That means that the cover that holds the tape hub in place is relatively free to move and which also means that the cover does not attenuate vibrations that are produced by the tape hubs in an efficient way.
FIG. 1 shows a tape cartridge 10 having a cartridge fixing location 12 between a first tape hub 14 and a second tape hub 16. The cartridge housing 18 above the tape hubs 14,16 is fixed at the fixing location 12 to the bottom cover 11 that, in turn, is fixed to the tape drive 13 at exposed portions 11a, 11b by fixing elements A,B,C,D, (shown schematically) for holding the portions 11a, 11b fixedly to the tape drive 13. Dashed lines 18a, 18b illustrate a vibrational mode of the cartridge housing, that allows the hubs 14, 16 to move in a vertical direction (indicated with arrow Y).
FIG. 5 illustrates a prior art driver geared spline 200 having male gears 202 inserted into a geared hub 210 having female gears 212, of a tape reel 214 which holds tape 216. In order to ensure sufficient engagement, the spline must be inserted a distance h2 into the geared hub 210. It would be desirable to reduce this distance h2 so that a more compact movement can be employed to engage and disengage drive spindles from reel hubs. According to these considerations, the mechanical design of the present art does not satisfy the special requirements in the field of linear recording for a highly stable mechanical design of the tape hubs and cartridge housing, that is necessary in order to obtain reduced variation of the tape position relative to the magnetic head and thus increased track density.